The invention relates to a valve for the metered introduction of fuel into engine in which the fuel is, volatilized from a fuel tank of an internal combustion engine.
Such valves are known for instance from German Patent Disclosures DE 40 23 044 A1 and DE 195 16 545 A1; they serve to regenerate adsorption filters for fuel vapor trapping systems for vehicle fuel tanks. These magnet valves have a hollow-cylindrical magnet core, which is joined to a valve seat body that forms the short-circuit yoke of the electromagnet, covers the magnet housing, and rests peripherally on an annular rib. Annular slits which form an opening cross section of defined size are disposed in the valve seat body.
Because of this structural design, a predeterminable volume of fuel vapors can be aspirated away, for a predetermined stroke of the valve member. This volume is defined by the maximum possible opening cross section of the hollow-cylindrical magnet core and of the opening slits in the valve seat. Slight variations can be compensated for by axial adjustment of the magnet core. Because of their structure, such valves are not suitable for large flow quantities, and in particular their use in direct gasoline injection engines is problematic.
German Patent DE 42 29 110 C1 discloses a device for temporary storage and metered feeding of volatile fuel components, located in the empty space of a tank system, into the intake tube of an internal combustion engine, in which the storage chamber communicates with the intake tube through a line that can be closed by a valve actuatable electromagnetically. The valve has one inlet opening and one outlet opening, and at least one valve seat that is closable by a closing member is provided between the inlet opening and the outlet opening. The valve seat forms the axial boundary of a tubular nozzle. In the region of the valve seat, this nozzle has a first opening cross section, which in the flow direction immediately downstream of the valve seat narrows to a second opening cross section. The second opening cross section is widened, on the side remote from the valve seat, in the region of the axial termination of the nozzle, to a third opening cross section that is larger than the first opening cross section.
In this device, the area of the first opening cross section is 1.01 to 2.5 times greater than the area of the second opening cross section. Because of these size ratios, quite a long valve stroke is required for pumping a certain predetermined quantity, which results in long opening and closing times. Furthermore, such a long stroke creates not inconsiderable background noise when the valve opens and closes.
The object of the invention is to further refine the valve of this generic type such that at large flow quantities, the valve functions with as little vulnerability to dirt and as noiselessly as possible, and that moreover the valve can be made economically and in particular can be used even in direct gasoline injection engines.
This object is attained, in a valve for the metered introduction of fuel volatilized from a fuel tank of an internal combustion engine, into the engine, of the type described at the outset. Because a flow element which throttles the flow of a gas and whose shape is adapted to the opening cross section of the sealing seat that cooperates with the valve member in such a way that the area of the opening cross section of the effective valve seat is greater than 2.5 and preferably greater than 9 times the area of the effective cross section of the flow element is disposed downstream of the valve member. It is possible, by the embodiment of the flow element and the sealing seat, for a predetermined stroke of the valve member, to set opening cross sections within wide limits, by adapting the opening cross section and the shape of the flow element to the opening cross section of the sealing seat. The above-indicated size ratios especially advantageously make it possible to attain a short valve stroke and thus short opening and closing times, with only slight background noise.
The flow element can be designed in the most various ways. In one advantageous embodiment, it is provided that the flow element is a throttle, whose cross section is smaller than the opening cross section of the sealing seat.
The flow element can furthermore also be a variable aperture, whose diameter is less than the opening cross section of the sealing seat.
Another advantageous embodiment contemplates a Laval nozzle, whose flow cross section is also smaller than the flow cross section of the sealing seat, as a flow element. With a Laval nozzle of this kind, in particular it is possible to generate an especially advantageous flow profile.
The seat element is preferably an armature plate, disposed in the valve member and forming part of the short-circuit yoke, on which advantageously elastic sealing and/or noise damping elements are disposed.
In an especially advantageous embodiment, it is provided that elastic damping elements protruding through the armature plate are disposed in the region of the sealing seat, and on the side toward the sealing seat the elastic damping elements have a sealing function and on the side toward the electromagnet the elements have a damping function. In this way, a sealing function can be combined with a damping function and thus especially the effort and expense of assembly for the sealing and damping elements and consequently the production costs can be reduced.
Another embodiment, which is especially advantageous in view of noise abatement in particular, provides that the seat element is an armature plate that includes two parts, which are embodied on one another, joined together, and provided with a sealing and/or noise damping element in such a way that a void is formed in the region of the sealing seat under the sealing and/or noise damping element. As a result of this void, the impact of the armature plate on the sealing seat is cushioned for the sake of reducing noise.
The impact of the armature plate, attracted by the electromagnet, on a pole plate of the electromagnet is advantageous cushioned by sealing and damping elements, which have a plurality of hollow-shaped rubber buttons which protrude through the armature plate and which upon opening of the valve, that is, when the armature plate is attracted by the electromagnet, strike the pole plate of the electromagnet.
In an especially advantageous embodiment of the invention, it is provided that the armature plate has a pressure equalization opening, which connects a void, embodied on one side of the armature plate toward the sealing seat, with a void (void toward the electromagnet) of the valve oriented toward the electromagnet and embodied on the other side of the armature plate. As a result, in an especially advantageous way, high switching frequencies are made possible, even in a valve with a sealing seat of especially large cross section. In valves with a large sealing seat, the prevailing differential pressure is in fact a problem, because it requires a very strong magnetic force if fast valve switching is to be made possible. Since the differential pressure in operation of the valve is dependent on the engine load of the vehicle, different attraction and closing times can result when the magnet force remains the same. By means of an armature plate that enables a pressure equalization, with a pressure equalization opening between a void toward the electromagnet and a void toward the sealing seat, a pressure equalization is made possible in a simple way.
The void embodied on the side of the armature plate toward the electromagnet is tightly closed off from the environment by an elastic sealing and damping element, which is secured to the magnet armature on its side toward the armature plate and executes a reciprocating motion together with the magnet armature.
The sealing and damping element protrudes the armature plate and thus advantageously also executes a sealing and damping function toward the sealing seat.
In order to preclude dirt particles and the like from reaching the interior of the valve during valve operation, an advantageous embodiment provides that a dirt trap concentrically surrounding the armature plate and is solidly structurally connected to the housing is provided, which traps dirt particles of predeterminable size in the opening direction of the valve and This dirt trap is preferably embodied in circular-annular form and has axially protruding, preferably cylindrical pins offset from one another. The pins are disposed adjacent one another in such a way that dirt particles of a predeterminable size are trapped by them.